In a large collaboration conducted via computers connected to networks, such as a webinar or on-line meeting, ensuring end-to-end security requires that each end-user (participant) be authenticated in an end-to-end fashion. The authentication cannot be done by the underlying infrastructure otherwise the end-users must trust the underlying infrastructure which is usually operated by a third party. This leads to the problem of scalability since one participant's computer resources are usually insufficient to authenticate a large number of participants in a reasonable amount of time.